# LeetCode 979. Distribute Coins in Binary Tree

https://leetcode.com/problems/distribute-coins-in-binary-tree/description/

## 題目大意

讓金幣均攤到二元樹上每個節點 (每個節點都一個金幣)

## 思考

因為可能會有新增跟移除 (正負)，所以在累加答案時要用絕對值

class Solution
{
public:
    int distributeCoins(TreeNode *root)
    {
        int ans = 0;
        dfs(root, ans);
        return ans;
    }

private:
    int dfs(TreeNode *root, int &ans)
    {
        if (!root)
            return 0;

        const int l = dfs(root->left, ans);
        const int r = dfs(root->right, ans);
        ans += abs(l) + abs(r);

        return root->val + l + r - 1;
    }
};